Locks



2 Sheets-Shadi'c l 55Min wall( Jan. l, 1963 A. R. BAKER ET AL LOCKS Filed May 27, 1959 Jan. l, 1963 A. R. BAKER ETAL LOCKS 2 Sheets-Sheet 2 Filed May 27. 1959 Patented Jan. 1, 1963 3,070,987 LOCKS Arthur R. Baker and Thomas F. Hennessy, Bristol, Conn., assignors to The American Hardware Corporation, New Britain, Conn., a corporation of Connecticut Filed May 27, 1959, Ser. No. 816,214 Claims. (Cl. '7G- 383) This invention relates generally to locks, and more particularly to improvements in operated, pin-tumbler lock cylinders of the type disclosed in the copending application of David Morrison, lr., Serial No. 814,253, filed May 19, 1959.

Pin-tumbler lock cylinders are used to a great extent in door locks, night latches, padlocks and many other types of lock-ing devices, bu-t those now in general use suffer the common disadvantage of having to be completely disassembled in .order -to change their pin-tumbler combinations. This generally requires the services of a skilled locksmith, and in cases where it is necessary to change the combinations `of a large number of lock cylinders, the task is both time consuming .and expensive.

-The above mentioned copending application discloses a unique and highly advantageous lock construction in which .the pin-tumbler combination of the lock cylinder may be changed Without disassembling the cylinder. However, such llock cylinders can only be used in locking devices which allow 180 rotation of the key-plug since it is necessary to bring the `open side of the keyway in said key-plug into alignment with the pin-tumbler holes in the housing of the lock cylinder in order to change lthe pin tumbler combination Many types of locking devices have mechanisms which are operable in and, in some instances, yallow less than 180 rotation of the key-.plug of .the lock cylinder therein, and it is apparent that lock cylinders constructed in accordance with the invention disclosed in said copending application cannot be conveniently used in such devices.

The primary object of the present invention is to provide a pin-tumbler lock cylinder whose combination may be changed by rotation of the key-plug through less than 180, and which is therefore well suited for use in those locking devices, particularly door locks, whose mechanisms are designed to operate in less than one-half turn of the key-plug.

.Another object of the invention is to provide a lock cylinder which is so constructed that one or more of the pin-tumblers initially provided therein may be permanently removed from operative position Without disassemblin-g the lock cylinder in order to change its pinturnbler combination.

A further object of the invention is to provide a lock cylinder whose pin-tumbler combination may be permanently changed simply by the use .of a regular key provided rfor .operating the lock cylinder.

,A most important object of this invention is to provide a master-keyed lock cylinder which is initially operable by a temporary master key, but which may be rendered unresponsive to said temporary master key with one of the regular keys provided for operating the lock cylinder.

Still another `object of the invention is to provide a master-keyed lock cylinder which is initially provided with at least one temporary pin-tumbler to permit operation of the lock cylinder by a temporary master key, but Ifrom which the temporary pin-tumbler may be removed through means provided in the key-plug to thereafter prevent operation of the lock cylinder by the temporary master key.

Another object of the present invention is to provide a construction for .changing the pin-.tumbler combination y of a lock cylinder without disassembly thereof which is .applicable to both regular master-keyed lock cylinders and to master-keyed lock cylinders including a masterring.

One of the most practical uses for lock cylinders embodying the present invention is in the door locks of a large buildin-g. During the construction of a building, each of the contractors is usually given a temporary or construction master key which will operate any one or all of the lock cylinders in the building lso that the contractor may enter the building at any time to perform his work. When the building has been completed, it is common practice to change the pin-tumbler combinations of the various lock cylinders therein so that they can no longer be operated by the temporary master key, thus preventing entry into the building by unauthorized or unscrupulous persons who might have gained possession of a temporary master key. Heretofore, it was necessary to .disassemble each lock cylinder in order to change its pin-tumbler combination, but with the present invention, the combinations of the lock cylinders may easily and quickly be changed by an authorized person possessing the proper key. p

Preferred forms of locks constructed in :accordance with the present invention are illustrated in the accompanying drawings wherein:

FIG. 1 lis an elevational view of a master-keyed, pintumbler lock cylinder, par-tly in central vertical section, showing the initial combination of pin-tumblers in the rst pin-bore.

FIG. 2 is .a sectional, end view of said lock cylinder taken on line Z-Z .of FIG. 1 and illustrating the construction of the key-plug.

FIG. 3 is an isometric view further illustrating the construction of the key-plug.

FIG. 4 is a fragmentary, elevational view of the lock cylinder, partly in central vertical section, illustrating the positions assumed by the pin-tumblers in the first pinibore when the temporary master key is inserted into the key-plug.

FIG. 5 is a diagrammatic view illustrating the positions assumed by said pin-tumblers when lthe permanent master key for the lock cylinder is inserted into the key-plug.

FIG. 6 is a fragmentary, elevation-a1 view of the lock cylinder, partially in central vertical section, illustrating the positions assumed by the pin-tumblers when the service key is inserted into the key-plug.

FIG. 7 is a sectional end view taken on line 7-7 of FIG. 6.

FIGS. 8, 9 and 10 are sectional end views similar to FIG. 7 illustrating the manner in which the pin-tumbler combination `of the lock cylinder is changed through the use 'of the service key.

FIG. 11 is -a diagrammatic view illustrating the positions .assumed by :the pin-tumblers when the penmanent master key is inserted into the key-plug after the combination of the lock cylinder has been changed.

FIG. 12 is a similar view illustrating the positions assumed by the pin-tumblers in response to the service key after the combination of the lock cylinder has been changed.

In the lock cylinders shown in the drawings, we have utilized only the first pin-bores to illustrate the novel features of our invention. It will be apparent to those skilled in the art, however, that the present invention may be incorporated in any one or more of the pin-bores of the lock cylinders disclosed, and also in many other types of pin-tumbler lock cylinders. YIn addition, many other combinations and arrangements of pin-tumblers may be used according to the particular keying system desired without departing from the spirit of the present invention.

n The lock cylinder illustrated in FIGS. 1 to 13 of the drawings is, for the most part, of the conventional pintumbler type, and includes a housing 5 having a cylindrical portion 6 and an integral, radially extending charnber fpor-tion 7. The cylindrical portion 6 of the housing contains an axial opening 8 and a longitudinally extending row of equally spaced pin-tumbler holes 9 which extend radially `from the opening 8 into the chamber portion 7.

A key-plug 10is rotatably mounted in the axial opening 8 and is provided at its outer end with a flange 11 which abuts the ou-ter end of the housing and prevents inward axial movement of the key-plugwith respect thereto. Axial movement of the key-plug 10 in an outward direction with respect to the housing 5- is prevented by a re taining ring 12 which is mounted in an annular groove -formed in the key-plug and abuts the inner end of the housing 5'. A blade 13 extends axially from the inner end of the key-plug and is adapted to engage and actuate the locking mechanism of the door lock or other locking device in which the lock cylinder is mounted.

The key-plug 10 contains a row of equally spaced, radially extendingpin-tumbler holes 14 in one side thereof andan axially extending keyway 15 in its opposite side which intersects said holes. The holes 14 are aligned with the holes 9 in the housing 5 when the key-plug is in its normal locked position, as illustrated in FIGS. 1 and 2 of the drawings, and -said holes form elongated pin-bores 167m the lock cylinder which communicate with the keyway 15.

Each of the pin-bores 16 slidably contains a plurality of conventional, axially aligned tumbler elements of predetermined heights which are arranged in series common to master-keyed lock cylinders. The lowermost tumbler element in each Vpin-bore comprises an anti-friction ball 17 which facilitates insertion and withdrawal of the keys for the lock cylinder, and above each ball 17 there is located 'a set of cylindrical pin-tumblers of conventional -form which includes a service pin 1S, a master pin 19 anda driver pin 20. A compression spring 21 is contained in each pin-bore and urges the tumbler elements therein toward the keyway 15. In the disclosed embodiment-of ythe present invention, the driver pin 20 in each pin-bore is normally disposed across the Shear line 22 of the lock cylinder defined by the peripheral surface of the keyeplug and the wall of the opening 8 in the lock cylinder housing.

`VIn the first pin-bore ofthe lock cylinder, where we have chosen to illustrate the present invention, we provide, in addition to the conventional tumbler elements, a temporary pin-tumbler 23 which, in this instance, is located between the service pin 18 and the master pin 19. Said temporary pin is cylindrical in shape, but is cross-sectionally `diierent than the conventional pin-tumblers 1S, 19 and 20 in that it is of a much smaller diameter. Said temporary pinis installed when the lock cylinder is initially assembled -to permit operation -thereof by a temporary master key-as will be hereinafter described. The temporary pin 23'is absent from the remaining pin-bores, but it willbe hereinafter understood that a similar temporary kpin could be used in any other or in all of the pin-bores tof-accomplish theobjects of the present invention.

In order to permit removal of the temporary pin 23 from its operative position in the lock cylinder, the keyplug 16 is provided with a radially extending, cylindrical recess or pocket 24 in its periphery which is aligned with and angularly spaced from 4the first pin-tumbler hole 14 therein. The diameter and the depth of the pocket 24 are slightly greater than the corresponding dimensions of the temporary pin 2.3i, but it Will be noted that the diameter of said pocket is still smaller than the diameter of the conventional pin-tumblers 18, 19 and 20a It will be seen from FIG. 2 of the drawing that, in the present case, the pocket 24 is located approx-imately 45 to the left of the rst pin-tumbler hole 14 in `the key-plug. Said recess could, of course, be located at any desired position around the key-plug depending on how far it is permitted to rotate, or a temporary pin 23 could be provided in any one or more of the pin-bores in the lock cylinder, and a corresponding pocket 24 could be provided in the key-plug on either or on both -sides of the pin-tumbler holes therein to permit the combination of the lock cylinder to be changed through rotation of the key-plug in either direction. There are many arrangements and combinations of temporary pins 23 and pockets 24 available as will be apparent to those skilled in the art.

The lock cylinder illustrated in FIGS. 1 to 13 of the drawings is originally provided with three keys; namely, a temporary master key 25, a permanent master key 26 and a service key 27. Each of said keys is of the well known type commonly provided with pin-tumbler lock cylinders, but only the outer end portion of each key has been shown in the drawings since We are primarily concerned with the pin-tumblers in the iirst pin-bore of the lock cylinder. It will be understood, however, that each of said keys is bitted to move the pin-tumblers in the pin-bores not shown to shear positon upon insertion thereof into the keyway 15.

In actual practice, only temporary master keys 25 are initially distributed with the lock cylinder since, with the particular arrangement of pin-tumblers in the first pinbore 16, the lock cannot be operated with the permanent master key 26, and the service key 27 is intended to be used only when'it is desired to change the combination of the lock cylinder so that it cannoth thereafter be operated by the temporary master key 25.

The first notch or bitting 25-a of the temporary master key 25 (see FIG. 4) 'is cut to such a depth that when said key is inserted into the keyway 15, the tumbler elements in the irst pinbore are moved to a position wherein the abutting ends of the driver pin 20 and the master pin 19 are aligned with the shear line 22 of the lock, thus permitting rotation of the key-plug. 'If the key-plug is rotated in a clockwise direction, as viewed in FIG. 2, the pocket 24 will pass under the end of the driver pin 20, but since said pocket is of a smaller diameter than the driver pin, said pin cannot enter the pocker vand there will be no interference with the rotation of the key-plug.

The depth of the rst hitting 26-a of the permanent master key 26 is such that said key Will operate the lock cylinder only after the temporary pin 23 has been removed from the rst pin-bore, and should an attempt be made'to operate the key plug with the permanent master key 26 while the temporary pin is in operative position, the master pin 19 will be disposed across the shear line 22 of the lock cylinder to prevent rotation of the key-plug as shown in'FlG. 5.

When it is desired to change the pin-tumbler combination of the lock cylinder so that it cannot be operated by the temporary master key 25, the service key 27 (see FIGS. 6 through 9) is inserted into the keyway 15. The iirst hitting 27-a of the service key is relatively shallow so that the tumblers in the first pin-bore will be lifted to a position wherein the abutting ends of the service pin 1S and the temporary pin 23 are aligned with the shear line 2.2 or" the lock cylinder as shown in FIGS. 6 and 7. The temporary pin 23 is thus disposed in the pin-tumbler hole 9 in the lock housing `adjacent the Yshearline -22 and the peripheral surface of the key-plug 10. The key-plug is then rotated in a clockwise direction from its normal position illustrated in FIG. 7 to the position shown in FIG. 8 to bring the pocket 24 into alignment with the rst pinturmbler hole 9 and the temporary pin 23, whereupon the spring 2l will urge the temporary pin 23 into said pocket. The master pin 19 is prevented from entering the pocket because of its larger diameter and will thus be disposed in shear position so as not to interfere with rotation of the key-plug. When the key-plug is rotated back to its normal position, the temporary pin 23 is carried from its operative position in the rst pin-bore and theerafter remains in the pocket 24, and the combinationy of the lock cylinder is changed. When the service key is withdrawn from the keyway, the tumbler elements in the first pin-bore will assume the positions illustrated in FIG. l0.

After the temporary pin 23 has been removed from the rst pin-bore in the manner above described, the lock cylinder may be operated by the permanent master key 26 and by the service key 27. yWhen the permanent master key is inserted into the keyway, the tumblers in the rst pin-bore will assume the positions illustrated in FIG. ll wherein the abutting ends of the driver pin 2t) and the master pin 19 are aligned with the shear line 22 to thus permit rotation of the key-plug. When the service key 27 is inserted into the keyway, the tumblers in the rst pin-bore are lifted to the position shown in FIG. l2 wherein the abutting ends of the service pin 18 and the master pin 19 are aligned with the shear line 22.

Should an attempt be made to operate the lock cylinder with a temporary master key 25 after the temporary pin 23 has been removed, the driver pin 20 in the rst pin-bore will not be lifted to shear position, but will be disposed across the shear line 22 of the lock cylinder, as shown in FIG. 13, and will thus prevent rotation of the key-plug. After the combinaton of the lock cylinder has been changed, rotation of the key-plug with the permanent master key or the service key is not impaired by the pocket 24, which now contains the temporary pin 23, since said pocket is of a smaller diameter than the conventional pin-tumblers and will thus pass thereunder as the key-plug is rotated.

In FIGS. 14 and 15 of the drawings, we have illustrated our invention embodied in a conventional masterring lock cylinder which includes a housing 28 having. a cylindrical portion 29 and an integral, radially extending chamber portion 30. The cylindrical portion 29 contains an axial opening 31 which terminates inwardly of the front end of the housing and rotatably receives the key-plug of the lock which, in this instance, comprises a master-ring 32, which is rotatable in the opening 31, and a key-barrel 33 which is concentric with the masterring and is rotatable therein. The housing, master-ring and key-barrel are provided with rows of equally spaced pin-tumbler holes which are normally aligned and form the pin-bores 34 of said lock cylinder. The key-barrel extends through an opening in the front of the housing and contains an axial keyway 35 whichintersects the pintumbler holes therein.

Each of the pin-bores 34 contains a set of conventional tumbler elements arranged in combinations common to master-ring lock cylinders and which includes an anti-friction ball 36, a service pin 37, a master pin 38 and a driver pin 39. The tumbler elements in each bore are urged toward the keyway 35 by a spring 40 and are normally located in a position wherein the driver pin 39 extends across the shear line 41 dened by the periphery of the master-ring and the wall of the opening 31, and the master pin 3S extends across the shear line 42 defined by the periphery of the key-barrel 33 and the wall of the opening in the master-ring.

The lock cylinder is adapted to be operated by a plurality of conventional keys which are bitted to move the pin-tumblers to shear position on either the shear line 41 or the shear line 42. When a permanent master key is inserted into the keyway, the driver pins and the master pins are moved to shear position on the shear line 41 and at least some of the master pins will be disposed across the shear line 42 so that the master-ring and the keybarrel will be locked together and will rotate as a single unit. If a service key is inserted into the keyway, the abutting ends of the service pins 37 and the master pins 38 will be aligned with the shear line 42 and the master pins will extend across the shear line 41 so that the keybarrel 33 will rotate independently of the master-ring.

In accordance with the present invention, we provide in the first pin-bore 34 of the lock cylinder a temporary pin 43 which may be identical to the temporary pin 23 previously described. Said pin is disposed between the master pin 38 and the driver pin 39 and normally occupies the position shown in FIG. 14. We also provide a pocket 44, similar to the pocket 24, in the periphery of the master-ring 32 which is aligned with and angularly spaced from the rst pin-tumbler hole therein and is adapted to receive the temporary pin. As above described, both the temporary pin 43 and the pocket 44 are of a smaller diameter than the conventional pin-tumblers so that no interference with the rotation of the masterring will be encountered at any time before or after the combination of the lock cylinder has been changed.

The lock cylinder is initially adapted to be operated by a temporary master key, not shown, which is so bitted that it will move the pin-tumblers to shear position on the outer shear line 41 with the abutting ends of the temporary pin 43 and the driver pin 39 aligned with said shear line to permit rotation of the master-ring and the key-barrel in unison. It will thus be obvious that when the temporary master key is used, the temporary pin 43 remains-in the pin-tumbler hole in the master-ring and moves around therewith.

The pin-tumbler combination of the master-ring lockl cylinder may be changed by inserting into the keyway 35 an appropriate master key 45 (see FIG. 15) which is bitted to move the tumblers in the rst pin-bore to a position wherein the abutting ends of the master pin 38 and the temporary pin 43 are aligned with the outer shear line 41 of the lock cylinder, thus positioning the temporary pin in the pin-tumbler hole in the cylinder housing and adjacent said shear line 41. It will be evident from FIG. 15, that, with the tumblers in this position, the key-barrel and the master-ring will rotate as a unit, and that as the pocket 44 in the periphery of the master-ring moves into alignment with the rst pintumbler hole in the lock housing, the temporary pin will` be projected into the pocket 44 so that it may be removed from operative position in the lock upon rotation of the key-barrel and the master-ring back to normal locked position. In this manner, the combination of the lock cylinder is changed so that it can no longer be operated by the temporary master key initially provided therefor, and anyone having possession of a. temporary master key will therefore be prevented from operating the locking device containing the lock cylinder.

We claim:

l. In a lock, a housing, a key plug mounted in said housing for movement between locking and unlocking positions and having a keyway, said housing and said key plug having tumbler holes therein which are alignable and form a tumbler bore communicating with said keyway, a series of tumbler elements movable in said bore to release position wherein movement of said key plug to unlocking position is permitted, a rst used key and a second change key insertable into said` keyway and bitted for cooperation with said series of tumbler elements, said series of tumbler elements initially including a temporary tumbler element sized to permit movement of said series of tumbler elements to a release position when either said rst key or said second key is inserted into said keyway so that said key plug is operable domes? by either; of saidv keys, and means including a recess in saidV key plug; for receiving and effecting` permanent removal of said temporary tumbler element from said seriesv of tumbler elements the first time said second key is used to operate said key plug whereby said temporary tumblery element is permanently removed from said series of tumbler elements to thereby provide a permanent new series of tumbler elements in said bore, the cross-sectional dimensionsA of said temporary tumbler element and said recess, in a direction transversely of said bore, being different from the corresponding dimensions of other tumbler elements inv said series whereby said other tumbler elements are prevented from entering said recess, said newY series of tumbler elements being moved to a locking position, wherein movement of said key plug tok unlocking position is prevented, when said rst key is inserted into said keyway thereby permanently pret venting operation of said key plug by said first key.

2.` The subject matter set forth in claim 1, wherein the transverse cross-sectional dimensions of said recess in the key plug substantially correspond to the said cross- Sectional dimensions of said temporary tumbler element.

3. The subject matter set forth in claim l, wherein said temporary tumbler element and said recess are crosssectionally smaller in said direction than said other tumbler elements in` said series.

4. In a lock, a housing having an opening therein, a key plug mounted in said opening for movement between locking and unlocking positions and having a keyway, said housing and said key plug having tumbler holes therein which are alignable and 4form a tumbler bore communicating wtih said keyway, a series of individual` 4tumbler elements of circular cross-Sectional shape movable in said bore to release position wherein movement of said key plug to unlocking position is permitted, a first used key and a second change key ensertab-le into said keyway and bitted for cooperation with said series of tumbler elements, Said series of tumbler elements initially including a temporary tumbler element sized to permit movement of said series of tumbler elements to a release position when either said rst key or said second key is insertedinto said keyway so that said key plug is operable by either of said keys, said temporary tumbler element being smaller in diameter than other tumbler elements` in said` series and moved -in-to the tumbler hole in said housing and adjacent said key plug when said second k-ey is inserted into said keyway, said key plug having a recess 4therein movable into register with the tumbler holel in ,said housing and dimensioned to receive only said temporary tumbler element therefrom, whereby said temporary tumbler element is removed from said series of tumbler elements in said recess upon movement of said key plug to thereby provide a new series of tumbler elements in saidv bore, said new series of tumbler elements being moved to a locking position, wherein movement of said key plug to unlocking position is prevented, when said rst key is inserted into said keyway thereby preventing operation of said key plug by said firs-t Ikey after removal of said temporary tumbler element.

5. The subject matter set forth in claim 4, wherein said recess is of circular cross-sectional shape and has a diameter substantially the same as the diameter of lsaid Atemporary tumbler element.

6'. In a lock, a housing having an opening therein, a key plug mounted in said opening for movement between locking and unlocking positions and having a keyway, said housing and said key plug having tumbler holes therein which are alignable and form a tumbler bore oommunicating with said keyway, a series of pin-tumblers slidable in said bore to release position wherein movement ofsaid key plug to unlocking position is permitted, a iirst used key and a second change key insertable into said keyway and bitted for cooperation with said series of pin-tumblers, said series of pin-tumblers' initially including a temporary pin-tumbler of a length to permit movement of said series of pin-tumblers to a release position when either said first key or said second key is inserted into said keyway so that said key plug is operable by either of said keys, said ltemporary pin-tumbler being ,smaller in diameter Athan other pin-tumblers in said series .and moved into the tumbler hole in said housing and adja- `cent said key plug when said second key is inserted into ,said keyway, said key plug having a recess therein mov- .able into register with Ithe tumbler hole in ,said housing upon movement of said key plug by said second key, said recess being of a width substantially equal to the diameter of said temporary pin-tumbler and of a depth to receive said temporary pin-tumbler, whereby said temporary pin-tumbler is removed from said series of pin-tumblers in said recess to thereby provide a new series of pintumblers in said bore, said new series of pin-tumblers being anoved to a locking position, wherein movement of said key plug to unlocking position is prevented, when said first key is inserted into said keyway thereby preventing operation of said key plug by said rst key after removal of sai-d temporary pin-tumbler.

7. In a lock, a housing having an opening therein, a key plug mountedin said opening for movement between locking and unlocking positions and having a keyway, v.said housing and said key plug having ltumbler holes therein which are alignable and form a tumbler bore communieating with said keyway, a series of individual tumbier elements movable in said bore to release positions wherein movement of said key plug to unlocking position is permitted, a rst used key and a second change key insertable into said keyway and bitted to move said series of tumbler elements, said series of tumbler elements initially including a temporary tumbler element sized to per- Init movement of said series of tumbler elements to a release position when either said first key or said second key is inserted into said keyway so that said key plug is operable by either of said keys, the cross-sectional dimensions of said temporary tumbler element, in a direction transversely of the axis of said bore, being different from the corresponding dimensions of other tumbler elements in said series and said temporary tumbler element being positioned in the tumbler hole in said key plug by said first key and in the tumbler hole in said housing and adjacent the surface of said key plug by said second key, said key plug having a recess therein opening to -said surface and spaced from its said tumbler hole, said recess being movable into register with the tumbler hole in said housing upon movement of said key plug by said second key and bein-g dimensioned to receive only said temporary tumbler element therefrom, whereby said temporary tumbler element is removed from said series of tumbler elements upon movement of said key plug to thereby provide a new series of tumbler elements in said bore,y said new series of tumbler elements being moved to a locking position, wherein movement of said key plug to unlocking position is prevented, when said rst key is inserted into said keyway thereby preventing operation of said key plug by said first key after removal of said temporary tumbler element.

8. In a lock, a housing having an opening therein and a tumbler hole extending radially from said opening, a key plug rotatable in said opening and having a radial tumbler hole in one side thereof and an axial keyway intersecting said hole, the tumbler hole in said key plug being alignable with the tumbler hole in said housing to form a tumbler bore communicating with said keyway and extending across the shear-line of said lock deiined by the adjacent surfaces of said key plug and said opening, a series of abutting tumbler elements slidable in said bore and including pin-tumblers, one of Which normally extends across said shear-line to lock said key plug against rotation, a first used key `and a second change keyeach having a blade portion insertable into said keyway and bitted to move said series of tumbler elements, said series of tumbler elements initially including a temporary ond key is inserted into said keyway, said key plug hav,-

ing a radial pocket therein spaced from its said tumbler hole and movable into register with the tumbler hole said housing upon rotation of s-aid key plug, said pocket being of substantially the same diameter as and of a depth to receive said temporary tumbler element when moved into alignment therewith, whereby said temporary tumbler is removed from said series of tumbler elements in said pocket to thereby provide a new series of tumbler elements in said bore, said new series of tumbler element-s being such that when said first key is inserted into said keyway, said new series of tumbler elements is moved to 10 a locking position, wherein one of said pin-tumblers is disposed across said shear-line, to prevent rotation of said key plug by said iirst key.

9. The subject matter set forth in claim 8, wherein said pocket is located less than 180 from the tumbler hole in said key plug.

10. The subject matter set forth in claim 8, wherein said key plug includes a cylindrical master ring rotatably mounted in said opening and said pocket is located in the peripheral surface of said master ring.

References Cited `in the tile of this patent UNITED STATES PATENTS 1,650,564 Wolff Nov. 22, 1927 l,650,568 Hurd NOV. 22, 1927 1,796,098 Hardy Mar. 10, 1931 2,059,129 Maxwell et al. Oct. 27, 1936 2,818,723 Levin Jan. 7, 1958 

6. IN A LOCK, A HOUSING HAVING AN OPENING THEREIN, A KEY PLUG MOUNTED IN SAID OPENING FOR MOVEMENT BETWEEN LOCKING AND UNLOCKING POSITIONS AND HAVING A KEYWAY, SAID HOUSING AND SAID KEY PLUG HAVING TUMBLER HOLES THEREIN WHICH ARE ALIGNABLE AND FORM A TUMBLER BORE COMMUNICATING WITH SAID KEYWAY, A SERIES OF PIN-TUMBLERS SLIDABLE IN SAID BORE TO RELEASE POSITION WHEREIN MOVEMENT OF SAID KEY PLUG TO UNLOCKING POSITION IS PERMITTED, A FIRST USED KEY AND A SECOND CHANGE KEY INSERTABLE INTO SAID KEYWAY AND BITTED FOR COOPERATION WITH SAID SERIES OF PIN-TUMBLERS, SAID SERIES OF PIN-TUMBLERS INITIALLY INCLUDING A TEMPORARY PIN-TUMBLER OF A LENGTH TO PERMIT MOVEMENT OF SAID SERIES OF PIN-TUMBLERS TO A RELEASE POSITION WHEN EITHER SAID FIRST KEY OR SAID SECOND KEY IS INSERTED INTO SAID KEYWAY SO THAT SAID KEY PLUG IS OPERABLE BY EITHER OF SAID KEYS, SAID TEMPORARY PIN-TUMBLER BEING SMALLER IN DIAMETER THAN OTHER PIN-TUMBLERS IN SAID SERIES AND MOVED INTO THE TUMBLER HOLE IN SAID HOUSING AND ADJACENT SAID KEY PLUG WHEN SAID SECOND KEY IS INSERTED INTO SAID KEYWAY, SAID KEY PLUG HAVING A RECESS THEREIN MOVABLE INTO REGISTER WITH THE TUMBLER HOLE IN SAID HOUSING UPON MOVEMENT OF SAID KEY PLUG BY SAID SECOND KEY, SAID RECESS BEING OF A WIDTH SUBSTANTIALLY EQUAL TO THE DIAMETER OF SAID TEMPORARY PIN-TUMBLER AND OF A DEPTH TO RECEIVE SAID TEMPORARY PIN-TUMBLER, WHEREBY SAID TEMPORARY PIN-TUMBLER IS REMOVED FROM SAID SERIES OF PIN-TUMBLERS IN SAID RECESS TO THEREBY PROVIDE A NEW SERIES OF PINTUMBLERS IN SAID BORE, SAID NEW SERIES OF PIN-TUMBLERS BEING MOVED TO A LOCKING POSITION, WHEREIN MOVEMENT OF SAID KEY PLUG TO UNLOCKING POSITION IS PREVENTED, WHEN SAID FIRST KEY IS INSERTED INTO SAID KEYWAY THEREBY PREVENTING OPERATION OF SAID KEY PLUG BY SAID FIRST KEY AFTER REMOVAL OF SAID TEMPORARY PIN-TUMBLER. 